Resin-processed thin paper for heat-sensitive stencil printing paper

ABSTRACT

A thin paper, which has a basis weight of 5 to 15 g/m 2  and a thickness of 10 to 50 μm and which comprises at least 10% by weight, based on paper-constituting fibers, of a drawn polyester fiber having a single filament fineness of 2.5 denier or less, a filament length of 15 mm or less and a birefringence (Δn) of at least 0.03. This thin paper comprises at least one member selected from the group consisting of urethane resins and epoxy resins at crossing points and surfaces of the filaments in an amount of 3 g/m 2  or less of the thin paper. This thin paper is a valuable as a heat-sensitive stencil printing paper.

TECHNICAL FIELD

The present invention relates to a thin paper for a heat-sensitivestencil printing paper. More particularly, the present invention relatesto a thin paper to be used as a porous support of a heat-sensitivestencil printing paper which is perforated and formed into a printingplate on receipt of heat from a thermal head or a xenon flash lamp.

BACKGROUND ART

As the porous thin paper used for a heat-sensitive stencil printingpaper, there are generally known (1) a Japanese paper formed from anatural fiber such as paper mulberry, paper bush or manila hemp(Japanese Examined Patent Publication No. 41-7623), (2) a paper formedfrom a regenerated cellulose fiber or synthetic fiber such as rayon,vinylon, polyester or nylon, (3) a mixed paper from a mixture of theabove-mentioned natural fiber and the above-mentioned regeneratedcellulose fiber or synthetic fiber (Japanese Examined Patent PublicationNo. 49-18728), and (4) a polyester paper obtained by hot-pressing by ahot rot roll a thin paper formed from a mixture of a polyester fiber andan undrawn polyester fiber as a binder fiber (Japanese Examined PatentPublication No. 49-8809).

These thin papers are defective in that they are deformed by changes inthe humidity and temperature to cause a change of the dimension orreduce the capabilities thereof. Accordingly, a method in which thechange of the dimension in the wet state is reduced (Japanese UnexaminedPatent Publication No. 61-254396) and a method in which a thin paper isimpregnated with a liquid of a synthetic resin and is treated with thesynthetic resin also acting as an adhesive for the thin paper and a film(Japanese Examined Patent Publication No. 55-47997) have been proposed.Furthermore, a method of forming a polyester paper having an excellentdimensional stability and heat resistance has been proposed (JapaneseUnexamined Patent Publication No. 58-76597 and Japanese UnexaminedPatent Publication No. 58-76598).

The thin paper to be used for a heat-sensitive stencil printing papermust have certain capabilities: i.e., (a) the ink permeability is goodand the formed image is sharp, and the image capability is excellent,(b) the printing durability is excellent, (c) the paper strength isexcellent and a falling of filaments is controlled, (d) littledeformation such as thermal shrinkage or a formation of wrinkles occursand printing can be an exact reproduction of an original.

None of the foregoing known thin papers, however, satisfies all of theserequirements.

The problems involved in the conventional thin papers are summarizedbelow.

The thin paper (1) using a natural fiber is unsatisfactory in that,although a dispersant or a tackifier is added at the paper-making step,"Japanese paper crush marks" based on an uneven dispersion of the fiberinhibit a permeation of an ink and defects or omissions appear in theformed image. Although a paper strength-increasing agent is generallyadded at the paper-making step, the paper strength is too low, and thusthe base paper is wrinkled and the printing durability is poor.

In the case of the paper (2) formed from a regenerated cellulose fiberor the paper (3) formed from a mixture of a synthetic fiber and anatural fiber, the dispersion uniformity of the fiber is improved, butsince the fixation of crossing points of the fiber is poor and the paperstrength is low, deformation readily occurs and a falling of filamentsis caused at the laminating or printing step, with the result that theimage and the printing durability are poor. According to the methoddisclosed in Japanese Unexamined Patent Publication No. 61-254396, thedimensional stability in the wet state is improved by incorporating apolyester fiber or a regenerated cellulose staple fiber and adding anepoxidized polyamide-polyamine resin at the paper-making step.Nevertheless, this method is still unsatisfactory in that the fixationof crossing points of the fiber is poor and the printing durability andimage are not satisfactory.

In the case of the thin paper (4) comprising a polyester paper, althoughthe preparation process is contrived so that polyester filaments aretightly bonded to one another, many crossing portions of filaments arenot bonded by the binder fiber and the fixation is poor. Furthermore,the thermal shrinkage caused by heat from a thermal head or the like islarge, and because of a deformation or wrinkling, the printing of anexact reproduction of the original is impossible. Moreover, the bondingbetween the heat-sensitive film and thin paper at the laminating step ispoor, and a problem arises of a partial peeling of the film, and as aresult, the image and printing durability are poor.

According to the method of the synthetic resin processing disclosed inJapanese Examined Patent Publication No. 55-47997, a resin having arelatively low softening point is used for exerting the function of theadhesive between the thin paper and the film, and therefore, it cannotbe considered that crossing points of the filaments are bonded with astrong resin having a heat resistance. Namely, since a softening of theresin occurs and the reinforcing effect is poor, the paper strength andprinting durability are not satisfactory.

DISCLOSURE OF INVENTION

The present inventors carried out investigations with a view toovercoming the above-mentioned defects of the conventional thin papersto be used for heat-sensitive stencil printing papers, and as a result,found that, by adding a specific resin to a thin paper comprising apolyester fiber drawn in a quantity exceeding a certain specific levelafter the paper-forming step, crossing points of the filaments can bebonded unexpectedly tightly and substantially uniformly without areduction of the permeation of an ink, i.e., the requirements for a thinpaper for a heat-sensitive stencil printing paper are satisfied.

In accordance with the present invention, there is provided a thin paperfor a heat-sensitive stencil printing paper, which has a basis weight of5 to 15 g/m² and a thickness of 10 to 50 μm and which comprises at least10% by weight, based on paper-constituting fibers, of a drawn polyesterfiber having a single filament fineness of 2.5 denier or less, afilament length of 15 mm or less and a birefringence (Δn) of at least0.03, wherein at least one member selected from the group consisting ofurethane resins and epoxy resins is present at crossing points andsurfaces of the filaments in an amount of 3 g/m² or less of the thinpaper.

BEST MODE OF CARRYING OUT THE INVENTION

As the polyesters constituting the thin paper, preferably a polyalkyleneterephthalate, more preferably polyethylene terephthalate, is used. Acopolyester in which a part of the acid component or diol component issubstituted with another component can be used. Furthermore, a polyesterfiber having the surface treated with an antistatic agent or adispersant or a polyester fiber having a film of a different resin filmformed on the surface thereof can be used.

In the thin paper of the present invention, a drawn polyester fiberhaving a single filament fineness 2.5 denier or less, a fiber length of15 mm or less and a birefringence (Δn) of at least 0.03 must occupy atleast a part of the constituent fibers. When the single filamentfineness of the drawn polyester fiber is larger than 2.5 denier, auniform ink permeability cannot be obtained. The single filamentfineness of the drawn polyester fiber is preferably 0.2 to 1.0 denier.When the fiber length is larger than 15 mm, the dispersion of the fiberis bad and the image is poor. The fiber length is preferably 3 to 8 mm.When the birefringence (Δn) is smaller than 0.03, the drawing of thefiber is insufficient and the thermal shrinkage becomes extremely large,deformation and wrinkling occur, and an image which is an exactreproduction of an original cannot be obtained. The birefringence (Δn)is preferably 0.07 to 0.20.

The above-mentioned drawn polyester must be incorporated in an amount ofat least 10% by weight, into the constituent fibers, and thepaper-making operation then carried out. When the amount of thepolyester fiber is smaller than 10% by weight, even if a urethane resinor an epoxy resin is added after the paper-making operation, anunexpectedly high paper strength cannot be obtained, a uniformdispersibility of the fibers cannot be attained, and a good texturehaving a reduced number of fiber bonds cannot be obtained. Furthermore,the image is poor. The amount incorporated of the drawn polyester fiberis preferably 20 to 100% by weight.

Where the thin paper is composed solely of the polyester fiber orfibers, to maintain in the thin paper a strength sufficient to resistthe paper-making and winding operations, preferably at least 10% byweight, especially 20 to 40% by weight, of the polyester fiber is apolyester fiber containing a resin component having a melting point of80 to 150° C. As the polyester fiber containing a resin component havinga melting point of 80 to 150° C., preferably a core-sheath fibercomprising a polyester fiber is used as the core and a low-melting-pointcomponent (having a melting point of 80° to 150° C.), especially apolyolefin or a copolyester, is used as the sheath. Furthermore, anundrawn polyester fiber having a low melting point can be used as thebinder fiber in combination with the polyester fiber.

As the thin paper-constituting fiber other than the polyester fiber,there can be mentioned customarily used bast fibers and/or regeneratedcellulose fibers. Preferably, natural bast fibers such as manila hempand flax, and regenerated cellulose fibers such as viscose process rayonfibers and cuprammonium process rayon fibers are used. In view of thedispersibility of the fiber and the bonding by entanglement, preferablythe single filament fineness of the regenerated cellulose fiber issmaller than 2.5 denier and the fiber length is smaller than 15 mm.

The thin paper must have a basis weight of 5 to 15 g/m² and a thicknessof 10 to 50 μm. When the basis weight is smaller than 5 g/m² or thethickness is smaller than 10 μm, the printing durability becomesextremely poor, and when the thin paper is set to a printing machine asthe heat-sensitive stencil printing paper, the rigidity and nerve aretoo low and the thin paper cannot be practically used. When the basisweight is larger than 15 g/m² or the thickness is larger than 50 μm, theink permeability becomes far too low and the image becomes poor, andthus good results cannot be obtained. Preferably, the basis weight is 8to 13 g/m², the thickness is 25 to 35 μm, and the density (baseweight/thickness) is 0.25 to 0.45 g/cm³. When the basis weight,thickness and density are within the above-mentioned ranges, the formedimage is especially sharp and the image is very good.

When making the thin paper of the present invention, customarily useddispersants and tackifiers (preferably, polyethylene oxide andpolyacrylamide), deforming agents, releasing agents, antistatic agents,paper strength-increasing agents at the paper-making agents and sizingagents can be incorporated.

The thin paper of the present invention retains at least one memberselected from a urethane resin and an epoxy resin on crossing points andsurfaces of filaments in an amount of 3 g/m² (3 g of the resin per m² ofthe thin paper) or less. Preferably, the strength of the resin isincreased by heating, to intensify a mutual bonding among filaments.

When the amount of the resin exceeds 3 g/m², apertures of the porousthin paper are covered with resin films and the ink permeability isgreatly reduced and the image becomes poor, and thus good results cannotbe obtained. The amount of the resin is preferably 0.2 to 2 g/m².

As the urethane resins and epoxy resins used in the present invention,there can be mentioned solvent solution type, water-soluble type and anwater-dispesible type (emulsion type) resins and the like. Furthermore,there can be mentioned non-reactive type and reactive type resins(including one-liquid type and two-liquid type resins; in the case ofthe two-liquid type, the reaction is carried out by using a crosslinkingagent and a crosslinking promoter) and the like.

Preferably, the urethane resins and epoxy resins are water-soluble typeor water-dispersible type resins. Heat reaction type water-solubleresins (a catalyst may be added) or self-emulsifiable type resins (maybe crosslinked in advance) are especially preferably used. In the caseof the water-soluble or water-dispersible type urethane resins and epoxyresins, gumming-up is controlled at the resin processing step, and anexcellent operation adaptability is attained. The tensile strengths ofthe urethane resins and epoxy resins used in the present invention arepreferably at least 100 kg/cm², more preferably at least 300 kg/cm².

As the method of the resin processing of the thin paper, a method ispreferably adopted in which the thin paper is impregnated or coated by agravure roll with a solution or emulsion of the urethane resin and/orthe epoxy resin. After the application of the resin solution oremulsion, the thin paper is dried by a hot air drier or a hot roll. Thedrying temperature is preferably 50° to 210° C. When a hot-pressingoperation is carried out by using a hot roll simultaneously with thedrying operation, the paper strength can be further improved.

In the resin processing, the concentration of the resin is veryimportant, and preferably the resin concentration in the processingliquid is 8 to 30% by weight, although the preferred concentrationdiffers to some extent according to the base weight of the porous thinpaper and the kind of the resin. When the resin concentration exceeds30% by weight, resin films are formed on apertures of the thin paper andthe permeation of an ink is inhibited, and the image is poor. If theresin concentration is too low, in the case of an aqueous type resin, anextreme wrinkling or shrinkage occurs in the thin paper and good resultscannot be obtained.

At the resin processing of the thin paper, a paper strength-increasingagent ordinarily used at the paper-making step (preferably an epoxidizedpolyamide-polyamine resin, an anionic polyacrylamide resin, etc.) or asizing agent can be used in combination with the urethane resin or epoxyresin.

The mechanism of highly improving the strength of the thin paper by theurethane resin and epoxy resin in the present invention is assumed to beas follows.

(1) At the time of the application, such as impregnation or gravurecoating, the solution (dispersion) of the resin is gathered at crossingpoints of filaments in the thin paper by the capillary phenomenon, and asufficient amount of the resin is accumulated in crossing points of thefilaments.

(2) The resin has a strong intermolecular cohesive force, and when thethin paper is heated and dried after the coating of the resin, the resinis fusion-bonded and solidified at crossing points of filaments, wherebythe strength of crossing points of the filaments is improved.

(3) The resin forms a film having an excellent toughness on the surfaceof the fiber and can bond filaments to one another.

(4) The isocyanate group or epoxy group possessed by the resin forms astrong bond with the functional group (such as --OH group or a carboxylgroup) possessed by the fiber. An especially high bonding strength isattained by the polyester fiber.

(5) When the drying temperature is elevated to a certain extent (toabout 50-210° C.), in the case of the non-reactive resin, the filmformed on the fiber becomes tough, and in the case of the reactiveresin, the reaction is enhanced, and the strength of the resin and thebonding force to the fiber is improved (it is considered that a partialreaction occurs between the resin and fiber).

Due to the foregoing functional effects, the strength among filaments ofthe thin paper is increased to a high level not attainable in theconventional thin papers, and it is considered that the paper strengthis improved almost to the level influenced by the strength of the fiberper se.

The various properties referred to in the present invention weredetermined according to the following methods.

(1) Imageability

A FIGURE of the first level of JIS having letter size squares having aside of 5 to 20 mm and circles having a diameter of 1 to 5 mm, whichwere smeared black, was used as the original. A polyester film having athickness of 2 μm was laminated as the heat-sensitive film (drawnthermoplastic synthetic resin film) was dry-laminated with the thinpaper of the present invention as the porous support by a dry laminatorusing "Byron 300" (dry-laminating adhesive supplied by Toyobo) to form aheat-sensitive stencil printing paper (hereinafter referred to as"master") (the same procedures were adopted in examples and comparativeexamples). Note, in Example 16, a substantially amorphous copolyesterhaving a thickness of 1.5 μm was used as the photosensitive film.

By using the above-mentioned master and original, a printing plate wasmade by a digital full-automatic stencil printing machine (Risograph007DPN) supplied by Riso Kagaku Kogyo), and the obtained prints wereevaluated in the following manner.

The evaluation was carried out with the naked eye and the image wasevaluated according to the following three-stage scale, ◯, Δ, and x:

◯: the print was as sharp as the original, and there was no linethickness unevenness in letters and no white omission found in any ofparts smeared black.

x: the print was different from the original in that lines werepartially broken, wrinkles were formed, line thickness unevenness wasfound in letters and letters were illegible, and the print could not bepractically used.

Δ: the print was in the intermediate state between ◯ and x, in whichalthough lines were partially broken and line thickness unevenness wasfound, letters were legible, and the print could be used.

(2) Printing durability

The printing durability was evaluated based on the number of prints,according to the following three-scale stage.

The printing operation was carried out by using the printing machinedescribed in (1) above, and the number of prints obtained before finebreaks, wrinkles and streaks were formed and it became impossible toobtain the same printability of letters, lines and black-smeared circlesas in the first print, was counted.

◯: 3,000 prints or more

Δ: 1,500 to less than 3,000 prints

x: less than 1,500 prints

(3) Paper strength

The tensile strength at break (JIS P-8113 and JIS P-8135) of the thinpaper in the paper-forming direction (longitudinal direction) wasdetermined under dry conditions and under wet conditions. At the testunder dry conditions, the test piece was allowed to stand under aconstant temperature (22° C.) and constant relative humidity (66%) for24 hours. At the test under wet conditions, the test piece was dipped inwater maintained at 15° C. for 20 minutes. The unit is kg/15 mm ofwidth.

(4) Thickness

The thickness was determined according to JIS P-8118.

(5) Gas permeability

The gas permeability was determined according to JIS P-8117, except that96 sheets of the thin paper were piled and the measurement was carriedout in this state. The unit is sec/300 cc.

(6) Rigidity

One end of the test piece of thin paper having a length of 50 mm in thepaper-forming direction (longitudinal direction) and a width of 15 mmwas held horizontally, and the rigidity was evaluated based on the angleformed between the line connecting the free end to the fixed end and thehorizontal line. The unit is ° (degree).

(7) Thermal shrinkage

Thin lines having a length of 60 mm were drawn on the test pieces (200mm×200 mm) of the thin paper in the paper-forming direction(longitudinal direction) and the transverse direction (lateraldirection). Before and after the heat treatment (200° C.×30 minutes),the length of each line was measured, and the shrinkage was determinedin either the longitudinal direction or the lateral direction. Beforeand after the heat treatment, the test piece was allowed to stand at aconstant temperature (22° C.) and constant relative humidity (66%) for 1hour, and the thermal shrinkage then determined.

(8) Falling of filaments

An adhesive cellophane tape (Celotape supplied by Nichiban K.K.) havinga width of 18 mm and a length of 30 mm was applied to the thin paper,and the adhesive tape was peeled. The evaluation was made based on thedegree of falling of filaments attached to the adhesive tape.

The evaluation was effected with the naked eye according to thefollowing three-stage scale, ◯, Δ and x:

◯: no substantial falling of filaments found and the image was notsubstantially adversely affected.

x: many filaments were attached to the surface (18 mm×30 mm) of theadhesive tape.

Δ: the state was intermediate between ◯ and x, and the test piece couldbe barely used as the thin paper.

The present invention will now be described with reference to thefollowing examples. Note, all of "%" in the examples are by weight.

EXAMPLES 1 to 8

(A) Manila hemp was alkali-cooked, washed with water, diluted with waterto a concentration of 3% and beaten to a freeness of 18° SR (JIS P-8121)by a beater. The obtained manila hemp was mixed with a polyester fibershown in Table 1 (the kind and characteristics are shown) uniformly at aratio shown in "Composition of Thin Paper" in Table 3. An epoxidizedpolyamide-polyamine resin was homogeneously added in the form of anaqueous solution in an amount of 2% based on the manila hemp, and themixture was formed into a thin paper having the basis weight, thicknessand density shown in "Basic Properties of Thin Paper" in Table 3, byusing a Cylinder Yankee.

The thin paper was dried by a Yankee drier maintained at 130° C. andwound in a roll.

(B) The wound roll of the thin paper was processed at a resinconcentration shown in "Basic Conditions of Resin Processing" in Table 3under conditions shown in "Resin for Resin Processing and Coating andHeating Conditions" in Table 2. The amount of the resin adhering to thethin paper after the processing is shown in "Resin Amount" in Table 3.

(C) The characteristics of the resin-processed thin paper obtained in(B) above are shown in Table 3.

EXAMPLE 9

The manila hemp used in Examples 1 to 8 in an amount of 60% washomogeneously mixed with 20% of a polyester fiber [PET(C)] shown inTable 1 and 20% of a viscose process rayon fiber [staple fiber (A);single filament fineness of 1.5 denier and fiber length of 5 mm] shownin Table 1, and the subsequent treatments were carried out in the samemanner as described in (A) of Examples 1 to 8 to obtain a wound roll ofa thin paper having characteristics shown in Table 3.

The resin processing and the determination of the characteristics werecarried out in the same manner as described in (B) and (C) of Examples 1to 8. The results are shown in Table 3.

EXAMPLES 10 to 16

Polyester fibers shown in Table 1 were homogeneously mixed in water at amixing ratio shown in "Composition of Thin Paper" in Table 3 and themixture was diluted with water so that the fiber concentration was 3%.An epoxidized polyamide-polyamine resin was added in an amount of 2%based on the polyester fibers in the form of an aqueous solution and apaper stock was prepared by mixing them homogeneously. The paper stockwas formed into a thin paper by using a cylinder Yankee machine. Thebasic characteristics of the obtained thin paper are shown in Table 3.

The thin paper was dried by a Yankee drier maintained at 130° C. andsimultaneously hot-pressed, and the dried thin paper was wound into aroll. The resin processing and the determination of characteristics werecarried out in the same manner as described in (B) and (C) of Examples 1to 8. The results are shown in Table 3.

COMPARATIVE EXAMPLES 1 to 3

A thin paper composed solely of the manila hemp used in Examples 1 to 8was prepared in the same manner as described in (A) of Example 1 to 8.The resin processing was not carried out, and the characteristics weredetermined in the same manner as described above. The results are shownin Table 4.

COMPARATIVE EXAMPLES 4 to 6

With respect to thin papers prepared in the same manner as described inComparative Examples 1 to 3, the resin processing and the determinationof the characteristics were carried out in the same manner as describedin (B) and (C) of Examples 1 to 8. The results are shown in Table 4.

COMPARATIVE EXAMPLE 7

A thin paper was prepared in the same manner as described in Example 9,except that the polyester fiber used in Example 9 was not used and theamount of the manila hemp was increased to 80%. The results are shown inTable 4.

COMPARATIVE EXAMPLE 8

A thin paper was prepared in the same manner as described in ComparativeExample 7, except that a cuprammonia process rayon fiber [staple fiber(B); single filament fineness of 1 denier and fiber length of 5 mm] wasused instead of the viscose process rayon fiber used in ComparativeExample 7. The results are shown in Table 4.

EXAMPLE 9

With respect to the thin paper prepared in the same manner as describedin Comparative Example 7, the resin processing and the determination ofthe characteristics were carried out in the same manner as described in(B) and (C) of Examples 1 to 8. The results are shown in Table 4.

COMPARATIVE EXAMPLES 10 to 14

The characteristics of the thin papers prepared in the same manner asdescribed in (A) of Examples 1 to 8 were determined in the same manneras described above without performing the resin processing. The obtainedresults are shown in Table 4.

COMPARATIVE EXAMPLES 15 and 16

The thin paper prepared in the same manner as described in (A) ofExamples 1 to 8 was dip-coated (the resin concentration in the liquidwas 10%) with an acrylic resin (Voncoat R-3380 supplied by DIC) or anSBR resin (Lacstar 3307 supplied by DIC), and the coated thin paper wasdried at 105° C. to effect the resin processing. The adhering amount ofresin and the characteristics were determined. The results are shown inTable 4.

COMPARATIVE EXAMPLES 17 and 18

The thin paper prepared in the same manner described as described inExamples 10 to 16 was hot-pressed by a hot roll maintained at 180° C.without performing the resin processing. The results of thedetermination of the characteristics of the obtained paper are shown inTable 4.

                                      TABLE 1                                     __________________________________________________________________________    Characteristics of Polymer Fibers                                                                             Film component of                                      Single filament                                                                        Fiber length                                                                         Birefringence                                                                        Surface Layer of                              Indication Name                                                                        fineness (denier)                                                                      (mm)   (Δn)                                                                           Polyester                                     __________________________________________________________________________    PET(A)   2        7      0.13       --                                        PET(B)   1        5.5    0.15       --                                        PET(C)   2.3      5      --     Modified polyester                                                            having a melting                                                              point of 110° C.                                                       (Soffit N720                                                                  supplied by                                                                   Kuraray Co.)                                  PET(D)   1.2      5.5    0.08   Polyethylene having                                                           a melting point of                                                            130° C.                                                                (film thickness = 2 μm)                    PET Binder                                                                             2.5      7      --     Undrawn polyester                             __________________________________________________________________________     PET(C), PET(D): Coresheath fiber                                              PET: Polyethylene terephthalate                                          

                                      TABLE 2                                     __________________________________________________________________________    Resin for Resin Processing and Coating and Heating Conditions                                                         Heating                                                                       Temperature                                Indication                    Coating                                                                            at Resin                              Kind name   Maker   Tradename                                                                             Type   Method                                                                             Processing                            __________________________________________________________________________    Urethan                                                                            Urethane (A)                                                                         Daiichi Kogyo                                                                         Superflex                                                                             Aqueous                                                                              Gravure                                                                            80-160° C.                     Resin       Seiyaku 100     emulsion                                                                             coating                                         Urethane (B)                                                                         DIC     Crysbon A717                                                                          Ethyl acetate                                                                        Gravure                                                                            80-140° C.                                         (Assistant                                                                            solution                                                                             coating                                                        NX/HN)  (2-liquid                                                                     type)                                                  Urethane (C)                                                                         DIC     Hydran AP-20                                                                          Aqueous                                                                              Dip  80-160° C.                                                 emulsion                                                                             coating                                         Urethan (D)                                                                          Daiichi Kogyo                                                                         Elastoron                                                                             Water-soluble                                                                        Dip  80-200° C.                                 Seiyaku H-38           coating                                    Epoxy                                                                              Epoxy (A)                                                                            Kuboko Paint                                                                          Sun Fast: E                                                                           Methylethyl                                                                          Gravure                                                                            80-140° C.                     Resin               Clear Enamel                                                                          ketone coating                                                                solution                                                                      (2-liquid                                                                     type)                                                  Epoxy (B)                                                                            Asahi Kasei/                                                                          AER661/ Methylethyl                                                                          Gravure                                                                            80-180° C.                                 Sanwa Kagaku                                                                          Sunmide#330                                                                           ketone coating                                                                solution                                                                      (2-liquid                                                                     type)                                             __________________________________________________________________________

    TABLE 3      Basic characteristics Basic conditions of resin Results of evaluation     of characteristics of thin paper processing   Paper Paper      Basic     Conc.    strength strength Gas Rigidity  Example Composition of weight     thickness Density  (%) Resin Image Printing (dry) (wet) permeability     (degree) Thermal No. thin paper (g/m.sup.2) (82 m) (g/cm.sup.2) Kind     (g/m.sup.2) Amount ability durability (kg/15 mm) (kg/15 mm) (sec) (-)     shrinkage        1 Manila hemp 80%/ 10.0 31.8 0.314 Urethane (A) 10 1.3 ◯     ◯ 1.07 0.57 1.0 6 0.15  PET(A)20% 2 Manila hemp 80%/ 10.5     41.9 0.250 Urethane (A) 20 1.8 ◯ ◯ 1.04 0.62 0.9     2 0.15  PET(A)30% 3 Manila hemp 40%/ 10.8 50.0 0.216 Urethane (D) 25 1.7     ◯ ◯ 1.01 0.61 0.8 3 0.14  PET(B)60% 4 Manila     hemp 80%/      9.2 31.4 0.293 Urethane (A) 25 1.2 ◯ ◯ 1.10     0.66 1.1 7 0.17  PET(C)20% 5 Manila hemp 70%/  9.7 32.0 0.303 Urethane     (C)  8 1.0 ◯ ◯ 1.21 0.75 1.1 6 0.17  PET(D)30% 6     Manila hemp 80%/  9.5 31.7 0.300 Epoxy (A)      8 0.9 ◯ ◯ 1.00 0.58 1.1 5 0.20  PET(A)20% 7     Manila hemp 80%/ 11.6 36.3 0.320 Epoxy (A)      8 0.8 ◯ ◯ 1.18 0.63 1.2 3 0.19  PET(A)20% 8     Manila hemp 90%/  7.2 25.5 0.282 Urethane (B) 17 1.2 ◯     ◯ 0.92 0.55 0.9 9 0.22  PET(B)10% 9 Manila hemp 60%/ 12.4     42.6 0.291 Urethane (D) 20 2.5 ◯ ◯ 1.05 0.67 1.0     2 0.20  Staple fiber  (A)20%/PET(C)20% 10  PET(A)80%/ 13.1 32.0 0.409     Urethane (A) 20 1.5 ◯ ◯ 1.35 1.16 1.6 33  2.1     PET binder 20% 11  PET(A)70%/ 11.2 29.8 0.376 Urethane (D) 25 0.7     ◯ ◯ 1.31 1.05 1.3 32  1.9   PET(C)30% 12     PET(B)85%/ 10.6 27.2 0.390 Epoxy (A) 10 1.2 ◯ ◯     1.12 1.01 1.3 32  1.8   PET(C)15% 13  PET(B)60%/ 12.9 31.5 0.410 Epoxy     (B) 10 1.0 ◯ ◯ 1.30 1.20 1.4 34  1.8   PET(C)40%     14  PET(A)70%/  7.0 15.4 0.455 Urethane (D) 25 2.0 ◯     ◯ 1.00 0.91 1.2 35  1.6   PET(C)30% 15  PET(B)60%/ 14.5 38.1     0.381 Urethane (D) 20 0.5 ◯ ◯ 1.44 1.27 1.6 37     1.5   PET(C)40% 16  PET(B)70%/ 12.2 28.5 0.428 Urethane (C)  8 1.0     ◯ ◯ 1.52 1.24 1.5 33  1.7        PET(C)30%

    TABLE 4      Basic characteristics Basic conditions of resin Results of evaluation     of characteristics of thin paper processing   Paper Paper     Compara-     Basic     Resin   strength strength Gas Rigidity   ative Composition     weight thickness Density  Conc amount Image Printing (dry) (wet)     permeability (degree) Thermal Falling Example of thin paper (g/m.sup.2)     (82 m) (g/cm.sup.2) Kind (%) (g/m.sup.2) ability durability (kg/15 mm)     (kg/15 mm) (sec) (-) shrinkage filament        1 Manila hemp  7.6 27.2 0.279 -- -- -- Δ X 0.31 0.09 1.0 26     0.30 X  100% 2 Manila hemp  8.3 32.3 0.257 -- -- -- Δ X 0.24 0.05     1.0 30 0.32 X  100% 3 Manila hemp 10.8 32.6 0.331 -- -- -- X X 0.50 0.19     1.9 10 0.30 X  100% 4 Manila hemp  8.9 30.6 0.291 Urethane (A) 25 1.3     Δ Δ 0.53 0.23 1.0 18 0.15 ◯  100% 5 Manila hemp     10.8 38.4 0.281 Epoxy (A)  8 2.6 X Δ 0.60 0.32 2.1 11 0.20     ◯  100% 6 Manila hemp 10.7 37.8 0.283 Urethane (B) 15 2.5 X     Δ 0.62 0.36 2.3 24 0.13 ◯  100% 7 Manila hemp  9.3     29.9 0.311 -- -- -- X X 0.41 0.28 2.0 27 0.25 X  80%/Staple  fiber(A)20%     8 Manila hemp 11.4 38.2 0.298 -- -- -- X X 0.64 0.17 2.5 12 0.22 X     80%/Staple  fiber(B)20% 9 Manila hemp 11.8 39.9 0.296 Epoxy (A) 20 0.5 X     Δ 0.69 0.19 2.2 13 0.18 Δ  80%/Staple  fiber(A)20% 10     Manila hemp  8.7 25.6 0.340 -- -- -- X X 0.47 0.16 1.5 23 0.20 X  80%/     PET(A)20% 11  Manila hemp  8.6 29.5 0.292 -- --  -- X X 0.17 0.06 1.2 24     0.20 X  70%/  PET(A)30% 12  Manila hemp  9.1 31.2 0.292 -- -- -- X X     0.04 0.02 1.3 30 0.25 X  40%/  PET(B)60% 13  Manila hemp  9.3 34.0 0.274     -- -- -- X X 0.44 0.18 1.0 10 0.18 X  80%/  PET(C)20% 14  Manila hemp     9.5 33.1 0.287 -- -- -- X X 0.46 0.20 1.0 12 0.22 X  70%/  PET(D)30% 15     Manila hemp 10.2 37.1 0.275 Acrylic 10 2.1 X X 0.59 0.29 1.3 17 0.17     Δ  80%/  resin  PET(A)20% 16  Manila hemp 10.4 39.1 0.266 SBR     resin 10 2.3 X X 0.61 0.23 2.5 20 0.18 Δ  80%/  PET(A)20% 17     PET(A)80%/ 12.2 29.7 0.411 Hot pressing Δ Δ 0.63 0.49 3.0 37 4     .0 X  PET binder    by hot roll  20%    (temp: 180° C.) 18     PET(A)70%/ 14.0 35.9 0.390  X X 0.35 0.21 2.8 45 4.5 X  PET(C)30%

Industrial Applicability

The thin paper of the present invention has the excellentcharacteristics described below, and therefore, is valuable as aheat-sensitive stencil printing base paper.

(1) The thin paper has an unexpectedly high strength as a poroussupport.

(2) The printing durability is high.

(3) Filaments are uniformly dispersed and the texture is very good.

(4) A sharp image having a high quality is formed at the printing step.

(5) The nerve is relatively strong and a formation of wrinkles and otherdefects is prevented at the printing step.

(6) Falling (dropping) of the fiber is drastically controlled.

(7) The shrinkage of a thin paper composed solely of a polyester can bereduced by a resin processing.

(8) A paper composed solely of a polyester can be simply prepared at ahigh yield.

I claim:
 1. A thin paper for a heat-sensitive stencil printing paper,which has a basis weight of 5 to 15 g/m² and a thickness of 10 to 50 μmand which comprises at least 10% by weight, based on paper-constitutingfibers, of a drawn polyester fiber having a single filament fineness of2.5 denier or less, a filament length of 15 mm or less and abirefringence (Δn) of at least 0.03, wherein at least one memberselected from the group consisting of urethane resins and epoxy resinsis present at crossing points and surfaces of filaments in an amount of3 g/m² or less of the thin paper.
 2. A thin paper for a heat-sensitivestencil printing paper as set forth in claim 1, wherein the thinpaper-constituting fibers are polyester fibers alone, and at least 10%by weight of the polyester fibers having on the surfaces thereof a resincomponent having a melting point of 80° to 150° C.
 3. A thin paper for aheat-sensitive stencil printing paper as set forth in claim 1, whereinthe thin paper is composed of a polyester and at least one memberselected from the group consisting of a natural bast fiber and aregenerated cellulose fiber.
 4. A thin paper for a heat-sensitivestencil printing paper as set forth in claim 1, 2 or 3, wherein theurethane resins and/or epoxy resins are water-soluble resins orwater-dispersible resins.